Liquids & SolidsLiquids & Solids

Chapter 10

Types of BondingTypes of Bonding

Intramolecular Intramolecular

• within the moleculewithin the molecule

•covalent bondingcovalent bonding

•ionic bondingionic bonding

IntermolecularIntermolecular

•between moleculesbetween molecules

•dipole-dipole forcesdipole-dipole forces

•hydrogen bonding hydrogen bonding

•London Dispersion ForcesLondon Dispersion Forces

When ice changes to liquid and then to vapor, the intramolecular forces (covalent bonds) stay intact, only the weaker hydrogen bonds between molecules weakenand break.

Intermolecular ForcesIntermolecular Forces

Forces between (rather than within) molecules.Forces between (rather than within) molecules.

- dipole-dipole attractiondipole-dipole attraction: molecules with dipoles : molecules with dipoles orient themselves so that “+” and “orient themselves so that “+” and “” ends of ” ends of the dipoles are close to each other. (1 % as strong the dipoles are close to each other. (1 % as strong as covalent or ionic.)as covalent or ionic.)

- hydrogen bondshydrogen bonds: dipole-dipole attraction in : dipole-dipole attraction in which hydrogen is bound to a highly which hydrogen is bound to a highly electronegative atom. (electronegative atom. (F, O, NF, O, N))

10_208

AttractionRepulsion

(a)

(b)

+– +–

+

–

+

–

–+

+

–

+

–

–

+–

+– +

Electrostatic interaction of two polar molecules.

The polar water molecule and hydrogen bonds among water molecules.

10_210

– 100

0

100

– 200

Bo

ilin

g p

oin

t ( °C

)

Period

2 3 4 5

H2 O

Group 6A

Group 7A

Group 5A

Group 4A

HF

NH 3

CH4

SiH4

GeH4

SnH4

HI

SbH3

H2Te

H2SH2Se

HClAsH3

HBr

PH3

The boiling points of the covalent hydrides of the elements in Groups 4A, 5A, 6A, & 7A.

London Dispersion ForcesLondon Dispersion Forces

- relatively weak relatively weak forces that exist among forces that exist among noble gas atoms and nonpolar molecules. noble gas atoms and nonpolar molecules. (Ar, C(Ar, C88HH1818))

- caused by caused by instantaneous dipoleinstantaneous dipole, in which , in which electron distribution becomes asymmetrical.electron distribution becomes asymmetrical.

- the ease with which electron “cloud” of an the ease with which electron “cloud” of an atom can be distorted is called atom can be distorted is called polarizabilitypolarizability..

10_211

Atom A Atom B

No polarization

Atom A Atom B

Instantaneous dipole on atom Ainduces a dipole on atom B

Atom A Atom B

(a)

+–

+– +–

No polarization

Instantaneous dipole on molecule Ainduces a dipole on molecule B

(b)

Molecule A Molecule B

Molecule A Molecule B

Molecule A Molecule B

H H H H+ +

+ +

+ +

+ +

+ +

+–+–

+–

H H H H

H H H H

Instantaneous and induced dipole moments between nonpolar molecules -- London Dispersion Forces.

Bonding Models for MetalsBonding Models for MetalsElectron Sea ModelElectron Sea Model: A regular array of metals in a : A regular array of metals in a “sea” of electrons.“sea” of electrons.

Band (Molecular Orbital) ModelBand (Molecular Orbital) Model: Electrons : Electrons assumed to travel around metal crystal in MOs assumed to travel around metal crystal in MOs formed from valence atomic orbitals of metal atoms.formed from valence atomic orbitals of metal atoms.

Conduction Bands: Conduction Bands: closely spaced empty molecular closely spaced empty molecular orbitals allow conductivity of heat and electricity.orbitals allow conductivity of heat and electricity.

Metal AlloysMetal Alloys

1.1. Substitutional AlloySubstitutional Alloy: some metal atoms : some metal atoms replacedreplaced by others of similar size. by others of similar size.

brass = Cu/Znbrass = Cu/Zn

Substances that have a mixture of elements and Substances that have a mixture of elements and metallic properties.metallic properties.

Metal AlloysMetal Alloys(continued)(continued)

2.2. Interstitial AlloyInterstitial Alloy: : Interstices (holes) Interstices (holes) in in closest packed metal structure are occupied closest packed metal structure are occupied by by smallsmall atoms. atoms.

steel = iron + carbonsteel = iron + carbon

3.3. Both typesBoth types: : Alloy steels Alloy steels contain a mix of contain a mix of substitutional (Cr, Mo) and interstitial substitutional (Cr, Mo) and interstitial (Carbon) alloys.(Carbon) alloys.

Substitutional Alloy

Interstitial Alloy

Network SolidsNetwork Solids

Composed of strong directional Composed of strong directional covalent covalent bonds bonds that are best viewed as a “giant that are best viewed as a “giant molecule”.molecule”.

- brittlebrittle

- do not conduct heat or electricitydo not conduct heat or electricity

- carbon, silicon-basedcarbon, silicon-based

graphite, diamond, ceramics, glassgraphite, diamond, ceramics, glass

10_229

Diamond(a)

Network solid structure of diamond.

Some Properties of a LiquidSome Properties of a Liquid

Capillary ActionCapillary Action: Spontaneous rising of a liquid : Spontaneous rising of a liquid in a narrow tube. in a narrow tube.

Viscosity: Resistance to flow (molecules with large intermolecular forces).

Some Properties of a LiquidSome Properties of a Liquid

Cohesive forces exist between molecules of a Cohesive forces exist between molecules of a liquid. Adhesive forces exist between the liquid. Adhesive forces exist between the liquid and its container.liquid and its container.

10_216

= Cl

= Na

Sodium chloride

(b)

= H2O= CDiamond Ice

(a) (c)

Three crystalline solids -- a) atomic solid, b) ionicsolid, and c) molecular solid.

SemiconductorsSemiconductors

- Conductivity is enhanced by Conductivity is enhanced by dopingdoping with group 3a or group 5a elements. with group 3a or group 5a elements.

- n-type semiconductorn-type semiconductor -- doped with atoms having more valence electrons -- doped with atoms having more valence electrons -- Phosphorus.-- Phosphorus.

- p-type semiconductorp-type semiconductor -- doped with atoms having fewer valence electrons -- doped with atoms having fewer valence electrons -- Boron.-- Boron.

- See Figure 10.31 on page 477 in Zumdahl.See Figure 10.31 on page 477 in Zumdahl.

A substance in which some electrons can A substance in which some electrons can cross the band gap.cross the band gap.

Vapor PressureVapor Pressure

. . . is the pressure of the vapor present . . . is the pressure of the vapor present at at equilibriumequilibrium..

. . . is determined principally by the size of . . . is determined principally by the size of the intermolecular forces in the liquid.the intermolecular forces in the liquid.

. . . increases significantly with temperature.. . . increases significantly with temperature.

Volatile liquids Volatile liquids have high vapor pressures.have high vapor pressures.

SublimationSublimation

•Change of a solid Change of a solid directly to a vapor directly to a vapor without passing through without passing through the liquid state. the liquid state.

•IodineIodine

•Dry IceDry Ice

•Moth BallsMoth Balls

Vapor PressureVapor Pressure

Low boiling pointLow boiling point

• high vapor pressure. high vapor pressure.

• weak intermolecular forces.weak intermolecular forces.

Low vapor pressureLow vapor pressure

• high molar masses.high molar masses.

• strong intermolecular forces.strong intermolecular forces.

Melting PointMelting Point

Molecules break loose from lattice points and Molecules break loose from lattice points and solid changes to liquid. (Temperature is constant solid changes to liquid. (Temperature is constant as melting occurs.)as melting occurs.)

vapor pressure of solid = vapor pressure of liquidvapor pressure of solid = vapor pressure of liquid

Boiling PointBoiling Point

Constant temperature when added energy is used Constant temperature when added energy is used to vaporize the liquid.to vaporize the liquid.

vapor pressure of liquid = pressure ofvapor pressure of liquid = pressure of surrounding surrounding

atmosphereatmosphere

Phase DiagramPhase Diagram

Represents phases as a function of temperature and Represents phases as a function of temperature and pressure.pressure.

critical temperaturecritical temperature: temperature above which the : temperature above which the vapor can not be liquefied.vapor can not be liquefied.

critical pressurecritical pressure: pressure required to liquefy : pressure required to liquefy ATAT the the critical temperature.critical temperature.

critical pointcritical point: critical temperature and pressure (for : critical temperature and pressure (for water, water, TTcc = 374°C and 218 atm). = 374°C and 218 atm).

10_247

Te

mp

era

ture

(°C

)

Time

– 20

0

20

40

60

80

100

120

140Steam

Water and steam

Water

Ice andwater

Ice

10_252

Pc = 218

1.00P3 = 0.0060

Tm T3 Tb

0 0.0098 100 374

Solid Liquid

Gas

Temperature ( ° C)

Pre

ssur

e (a

tm)

Triplepoint

Criticalpoint

Tc

Phase diagram for water -- Tm is the regular meltingpoint. The solid/liquid line has a negative slope.

10_255

Pc =

72.8

1.00

P3 =

5.1

Tm T3 Tc

Solid

Liquid

GasTriplepoint

Temperature (°C)

– 78 – 56.6 31

Pre

ssur

e (a

tm)

Criticalpoint

Phase diagram for carbon dioxide -- the solid/liquid line has a positive slope.

10_257

Diamond

Graphite

Liquid

Vapor

107

109

1011

0 2000 4000 6000

Temperature (K)

Pre

ssur

e (P

a)

Phase diagram for carbon -- note the two solid forms of diamond and graphite.